# Ciphertext Malleability Issue in Tink Java

Advisory record · `GHSA-g5vf-v6wf-7w2r`

- **Identifiers:** `GHSA-g5vf-v6wf-7w2r` · `CVE-2020-8929` · `PYSEC-2020-142`
- **State:** Confirmed
- **Severity:** CVSS 5.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-176](https://cwe.mitre.org/data/definitions/176.html) · [CWE-327](https://cwe.mitre.org/data/definitions/327.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md) · [CWE-176](https://agentprime.io/advisories/tag/cwe-176.md)
- **Published:** 16 Oct 2020
- **Updated:** 8 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 16 Oct 2020, 00:51 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `com.google.crypto.tink:tink` (Maven): affected `<1.5.0`; fixed in `1.5.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Tink's Java package com.google.crypto.tink:tink before 1.5.0 let an attacker alter the key ID bytes of a ciphertext so that a second, different ciphertext decrypts to the same plaintext. The advisory says this matters mainly for deterministic AEAD used with a single key, and that confidentiality and plaintext integrity are not affected. Upgrade to version 1.5.0 or later; the advisory lists no workaround other than applying the fix.

Written 2 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`, from CNA (Google)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0046, the 40th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:20 UTC: First seen by agentprime
- 31 Oct 2026, 14:20 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-g5vf-v6wf-7w2r)

## Sources

- [GitHub Advisory Database: GHSA-g5vf-v6wf-7w2r](https://github.com/advisories/GHSA-g5vf-v6wf-7w2r)
- [OSV: GHSA-g5vf-v6wf-7w2r](https://osv.dev/vulnerability/GHSA-g5vf-v6wf-7w2r)
- <https://github.com/google/tink/security/advisories/GHSA-g5vf-v6wf-7w2r>
- <https://nvd.nist.gov/vuln/detail/CVE-2020-8929>
- <https://github.com/google/tink/commit/93d839a5865b9d950dffdc9d0bc99b71280a8899>
- <https://github.com/pypa/advisory-database/tree/main/vulns/tink/PYSEC-2020-142.yaml>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-g5vf-v6wf-7w2r>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-g5vf-v6wf-7w2r/>. Everything for agents: <https://agentprime.io/llms.txt>.